Choke coil, resistor, or the like



1944- H. N. VELEY 2,355,611

CHOKE COIL, RESISTOR, OR THE LIKE Filed March 15, 1943 /w A ra/\W/r/v$s.- Wm fla 15 1 Patented Aug. 15, 1944 cnoxn com, ansrs'ron, onTHE LIKE Hugh N. Veley, St. Marys, Pa., assignor to Speer ResistorCorporation, St. Marys, Pa., a corporation oi Pennsylvania ApplicationMarch 15, 1943, Serial No. 479,213

8 Claims.

This invention relates to a choke coil or resister or the like and tomethods of making the same, the invention being applicable to theformation of small electrical elements in which a wire is coiled about aform. In the case of a choke coil for high frequency purposes, the wirethus coiled may have low resistance; on the other hand, when a wirewound resistor is provided, the wire may be of conventional highresistance type.

It has been customary to provide as high frequency chokes small coilswound on forms in single or multiple layers offering high impedances atradio frequencies. Such coils have been wound on insulating supports ofBakelite or other thermoplastic or thermosetting resins. There isinvolved a problem of anchoring the coil ends so that the coil will notaccidentally unwind or shift in position, with resulting changes in itsimpedance. It has, therefore, been customary to provide elaborate typesof terminals to serve as anchorages for the coil ends. In the case ofwire wound resistances, similar complications were involved in anchoringthe coil ends.

It is one object of the present invention to provide an improved andsimple coil arrangement whereby the ends of a coil, constituting a chokecoil or resistance, may be anchored in simple fashion to maintainconstant the impedance value of the coil despite rough handling.

This object and further objects relating to the methods of forming suchproducts and to details of construction, will become apparent from thefollowing description, read in conjunction with the accompanyingdrawing, in which:

Figure 1 is a view partially in section showing a choke coil or wirewound resistor formed in accordance with the present invention;

Figure 2 is an end view of the same with the insulation omitted;

Figure 3 is a diagrammatic sectional view showing the fashion in whichthe insulating support is simultaneously molded and provided withwire-holding notches; and

Figure 4 is a fragmentary sectional view of a modified form of theinvention in which a coil is shunted by a molded resistor.

Referring first to Figures 1 and 2, what is illustrated therein may beregarded as either a choke coil or resistor or combination thereof,

depending upon the resistance of the coil of wire which is used. Asillustrated in that figure, the product comprises a form 2 desirablymade of molded thermosetting or thermoplastic resin,

preferably the former, if the product is a wire wound resistor, thoughpossibly the latter if the temperature rise of the resistor is notexpected to be too great, or if the product is merely a high frequencychoke. Molded into the ends of this form 2, as will be indicatedhereafter, are wire terminals 4. Adjacent the terminals 4 and in theends of the form 2 there are provided in the molding process notches 6,preferably taking the form illustrated and providing edges I extendinglongitudinally of the form. About the form there is wound the low orhigh resistance wire 8, de-

Y lar about the sharp corners 1 formed by these notches, a copper orother wire, having little spring action, will be very securely fastenedmerely by having its free ends twisted about the terminal wires 4 asindicated, there being little chance that the wire will be disturbed inany ordinary handling of the element unless a special effort in thatdirection is made. The wire ends may be further secured by soldering orwelding.

Generally speaking, the product, to the extent described, may be thefinal one. However, in some cases, it may be desirable to coat this poduct with insulation as indicated at M, for which purpose injectionmolding by Bakelite or other similar resin may be utilized, the wirewound lements being located in suitable molds supported by theirterminal wires and surrounded by the plastic material in the moldingprocess. Alternatively, a thin insulating coating may be painted orsprayed thereon.

While in the product illustrated in Figure 1 there is shown only asingle layer of winding, it will be obvious that the invention i equallyapplicable to multi-layer coils. The invention is further applicable tothe making of non-inductive resistors by winding on the form a doublelength of wire, the ends being anchored in the respective notches asindicated. Various other fashions in which the principles of theinvention may be utilized will be apparent to the art.

The formation of the body in a simple molding operation is illustratedin Figure 3. Die and plunger elements are indicated at I8 and 2|,respectively, the plunger elements being duplicated, as will be evidentfrom consideration of the method more fully set forth in the applicationof Herrick and Veley, Serial No. 424,250, filed December 24, 1941. Upperand lower plungers designed to enter the upper and lower ends of theopening in the die ll carry the terminal wires 4, which may be providedwith bent heads such as indicated at IQ for the purpose of affordinggood anchorage and, in the instance hereafter described, good electricalcontact with a molded resistor body. The plungers 2. are provided withprojections 2|, which form the notches 4 during the molding operation.The molding may be carried out as described in said Herrick and Veleyapplication, simplified in the case such as that illustrated, in whichthe form is a simple cylinder of resistance material.

The invention is further applicable to the formation of elements inwhich a coil of wire is to be shunted by a resistance which may take theform of a molded resistor. For example, in the case of resistorsdesigned to provide multiple ranges for meters, if the series resistorsto be used have quite high resistance, the resistance of the meter mayfrequently be neglected. On the other hand, suppose, for example, that amilliammeter is to be used as a voltmeter having a resistance of 1,000ohms per volt and a scale of volts. Under such circumstances, if therewas included in series with the meter only a resist ance of 10,000 ohms,the resistance of the meter itself would introduce an error. To makeallowance for the meter resistance, an accurate wire wound resistor 01',say, 10,000 ohms, a standard value, may be shunted by a relatively highresistance molded resistor to give an external resistance, which, takenwith the resistance of the instrument itself, will be 10,000 ohms to ahigh degree of accuracy. In accordance with the invention, standard wireand standard wire winding procedure may be used to provide seriesresistors for particular instruments by providing a reduction ineffective resistance equal to that of the resistance of the meter coilsby adopting the procedure of shunting the wire winding with a highresistance molded resistor body, the accuracy of the resistance value ofwhich need not be particularly great. Figure 4 illustrates a product ofthis type. This comprises essentially a molded resistor of the typedisclosed in' said Herrick and Veley application and comprising aninsulating shell 2 and a molded resistor portion 24, inside said shell,comprising the usual composition of plastic and conducting material suchas graphite or the like, or possibly including materials serving to givea negative temperature coefllcient value to the resistor. Into theconductive material 24 there are molded leads 26 having bent ends of theform illustrated at 28 serving to hold the leads securely in positionand arranged to insure uniform penetration in the resistor formation.Molded in this case into both the insulating shell and the resistormaterial 24 are notches ll of the type heretofore described at i toserve for the anchorage of the ends of the wire winding 32, which endsare twisted about the leads 26 as indicated at 34, it being understoodthat the construction illustrated in Figure 4 is duplicated at theopposite end of the resistor. Under such circumstances, the winding 32may make up to a high degree of accuracy the major portion of theresistance to be used in series with the meter, for example, the windingmachinery may be adjusted ,to provide a definite length of resistancewire having, say, a resistance or 10,000 ohms, to a high degree ofaccuracy. If accurate wire wound resistors of this value are to beprovided, the machinemaybeusedtowindsuchwiresoneolid Bakelite or otherinsulating cores, as in Figure 1. On the other hand, if call arises toprovide resistors to be used in series with some particular instruments,it is only necessary then to wind the same wire on a resistor of thetype indicated, providing a shunting resistance causing the combinationto have a resistance of 10,000 ohms less the resistance of theinstrument.

It will be evident, also, that the resistor may thus be caused to shunta choke under conditions where a choke coil is to have an impedancevariation with frequency other than that which would be secured by theuse of a simple choke winding alone; i. e., such that for lowfrequencies the combination acts as a reactance with a resistancesubstantially only that of the low resistance coil, and for highfrequencies as a resistance with low reactance.

It will be evident that a combination of the type illustrated in Figure4 may be externally insulated by injection molding or the like, asindicated in the modification of Figure 1.

What I claim and desire to protect by Letters Patent is:

1. In combination, a molded plastic support having molded therein leadsextending axially therefrom and notches adjacent to said leads, saidsupport being at least partially conductive to afford conductivitybetween said leads, and a wire winding about said support having itsends bent into said notches, and coiled about said leads so that thewinding is thereby fixedly anchored in place.

2. In combination, a molded plastic support having molded therein leadsextending axially from the ends thereof and notches formed in the endsadjacent to said leads, and a wire winding about said support having itsends bent into said notches and coiled about the portions of said leadsextending axially from the ends of said support adjacent to said ends,so that the winding is thereby fixedly anchored in place.

3. In combination, a molded plastic support having molded therein leadsextending axially from the ends thereof and notches formed in the endsadjacent to said leads, the notches presenting axially extending edges,and a wire winding about said support having its ends bent sharply aboutsaid edges into said notches and coiled about the portions of said leadsextending axially from the ends of said support adjacent to said ends,so that the winding is thereby fixedly anchored in place.

4. In combination, a molded plastic support having molded therein leadsextending axially from the ends thereof and notches formed in the endsadjacent to said leads, and a wire winding about said support having itsends bent into said notches and coiled about the portions of said leadsextending axially from the ends of said support adjacent to said ends,so that the windin is thereby fixedly anchored in place, ands coating ofinsulation covering said winding.

5. The method of forming a mounted coil comprising molding a plasticsupport member by application of pressure to a molding powder whileinserting therein wire leads to cause the same to extent axially fromthe support and simultaneously forming notches in the ends of thesupport extending adjacent to the axially extending portions of theleads, and thereafter winding a wire about said support with its endsbent into said notches and coiled about the portions of said leadsextending axially from the ends of said support adjacent to said ends.

6. A winding form comprising a molded plastic support having moldedtherein leads extending axially from the ends thereof and notches formedin the ends adjacent to said leads, said notches being arranged toanchor the ends of a winding bent into said notches and coiled about theportions of said leads extending axially from the ends of said supportadjacent to sa d ends.

7. A winding form comprising a molded plastic support having moldedtherein leads extending axially from the ends thereof and notches formedin the ends adjacent to said leads, the notches presenting axiallyextending edges, said notches being arranged to anchor the ends of awinding bent sharply about said edges into said notches and coiled aboutthe portions of said leads extending axially from the ends of saidsupport adjacent to said ends. I

8. In combination, a molded plastic support of cylindrical form and ofsubstantially uniform diameter having molded therein leads extendingaxially from the ends thereof and notches formed in the ends extendingfrom points adjacent to said leads to the cylindrical surface of saidsupport and providing thereat axially extending edges, and a wirewinding about the cylindrical surface of said support having its endsbent sharply about said edges into said notches and coiled about theportions of said leads extending axially from the ends of said supportadjacent to said ends, so that the winding is thereby fixedly anchoredin place.

HUGH N. VELEY.

